This disclosure is generally in the field of antimicrobial polymeric materials and devices useful in the purification of fluids.
There remains a need for devices and methods to eliminate microorganisms from fluids for various applications, including the provision of safe or potable drinking water and breathable purified air. Many different methods are currently used for the purification of fluids. Representative examples include distillation, ion-exchange, chemical adsorption, filtering, and retention. Oftentimes, a number of different techniques must be combined to provide complete purification of fluids. These techniques can be costly, energy inefficient, and require significant technical expertise. Unfortunately, many low cost purification techniques do not adequately treat or remove harmful biological contaminants, bacteria, and viruses.
The U.S. Environmental Protection Agency (EPA) has set forth minimum standards for acceptance of a device proposed for use as a microbiological water filter. Common coliforms, represented by the bacteria E. coli and Klebsiella terrigena, must show a minimum 6-log reduction (99.9999% of organisms removed) from an influent concentration of 1×107 per 100 mL of water. Common viruses, represented by poliovirus 1 (LSc) and rotavirus (Wa or SA-11), which show a resistance to many treatment processes, must show a minimum 4-log reduction (99.99% of organisms removed), from an influent concentration of 1×107 per 100 mL of water. Cysts, such as those represented by Giardia muris or Giardia lamblia, are widespread, disease-inducing, and resistant to most forms of chemical disinfection. A device claiming cyst-removal must show a minimum 3-log reduction (99.9% of cysts removed) from an influent concentration of 1×106 per L or 1×107 per L.
Various water soluble antimicrobial chemical agents are known in the art. Representative examples of such conventional materials include soaps/detergents, surfactants, acids, alkalis, heavy metals, halogens, alcohols, phenols, oxidizing agents and alkylating agents. Most of these agents chemically alter (e.g., by an oxidation reaction, etc.) the cellular structure of microbes to inactivate them. Strong oxidants, such as phenols and hypochlorites, may effectively negate the potential threat of all microorganisms in water; however, unacceptable residual levels of these agents and/or their byproducts remain in the treated water and generally must be removed before the treated water can be consumed or used in other applications.
One conventional biocompatible antimicrobial agent is chlorhexidine. Chlorhexidine is a 1,6-di (4-chlorophenyl-diguanido) hexane having the chemical formula:

The IUPAC name for chlorhexidine is N,N″Bis(4-chlo-rophenyl)-3,12-diimino-2,4,11,13-tetrazatetradecanediim-ideamide. Chlorhexidine has a high level of antibacterial activity and low mammalian toxicity. Historically, chlorhexidine has been used in fluid treatment only in its soluble salt forms. Chlorhexidine salts, however, have an extremely bitter taste that must be masked in formulations intended for oral use. The rate of reaction for the soluble chlorhexidine salts or its conventional derivatives is second-order, as the reaction depends on both the concentration of chlorhexidine and the active sites of microorganisms. It would be desirable to provide an antimicrobial material which functioned effectively as a zero order reaction.
One conventional antimicrobial system for fluid treatment that does not involve the use of water soluble antimicrobial agents utilizes ultraviolet (UV) radiation. Such systems, however, require a source of electric power, are costly, and may not effectively inactivate microorganisms in a range of fluid types.
Accordingly, there remains a need for inexpensive and biocompatible antimicrobial materials and devices that can effectively inactivate microorganisms in fluids. It would be desirable for the antimicrobial material to work effectively as an antimicrobial material without being water soluble, so as not to detrimentally impact the quality of the aqueous fluid to be filtered and in order to avoid having to remove the residual antimicrobial material or by products from the treated fluid. It would be further desirable for the material to be readily adaptable for use in various conventional flow-through fluid filtration/purification systems, without the need for an additional power source. Desirably, the purification material would significantly exceed the minimum EPA requirements for designation as a microbial water purifier such that it is suitable for consumer and industry point-of-use applications.